Ask your system architect if it's useful to have a PLL vendor
with a huge range of flexible, off-the-shelf PLLs. Does it matter
if the vendor has a dedicated design team available both to help
you design the simplest possible clocking scheme, and to design
custom PLLs if your problem resists a simple clocking scheme?

Consider for yourself the
nature of the licensing terms, whether it obligates you to lingering
royalties or special multiple-use pricing. Does the vendor need a
test chip? Yours, perhaps?

Ask your vendor qualification people if you can switch foundries without requalifying
your PLL vendor. Such changes are only possible if the PLL
vendor's complete range of products are available to you on a broad range
of processes from several foundries.

Ask the person responsible for timing closure about the value of a very
low-jitter clock source. Ask that person how much it matters if the
PLL vendor has fully characterized their design. Ask that person if
they even believe the performance specifications claimed by your current
PLL vendor.

Ask your bring-up team what it's like to work with a prototype with an
unreliable clock source that has to be fixed in a second spin of the
chip. Does it help if the PLL works well even outside the specified
frequency range, even in bad packaging, or in the presence of
unexpected noise?